NH4+ Lewis Structure
Ammonium ion · What ammonia becomes when it accepts a proton, and the cation in most nitrogen fertiliser.
The NH4+ Lewis structure has 8 valence electrons - the 1+ charge removes one, drawn as four bonds to hydrogen, with zero lone pairs in total, all inside square brackets. The central N is sp3 hybridized, which makes it a tetrahedral ion with a bond angle of 109.5 degrees. The 1+ charge is written on the N, because that is the atom whose formal charge comes out positive - it is sharing more electrons than a free N atom owns. The charge belongs to the ion as a whole, which is what the brackets around the drawing mean.
- 8 valence e−
- tetrahedral
- 109.5° bond angle
- sp3
- 1+ charge
NH4+ molecular geometry
Tetrahedral, from 4 electron domains on the central N: 4 bonded atoms (AX4). The electron geometry is tetrahedral. Wedges point toward you, hashed wedges away. Every shape in the VSEPR chart →
Calculated properties
| Total valence electrons | 8 |
|---|---|
| Bonding electrons | 8 (4 shared pairs) |
| Nonbonding electrons | 0 (0 lone pairs) |
| Lone pairs on N | 0 |
| Electron domains (steric number) | 4 |
| VSEPR notation | AX4 |
| Electron geometry | tetrahedral |
| Molecular geometry | tetrahedral |
| Bond angle | 109.5° |
| Hybridization | sp3 |
| Charge | 1+ |
| Charge distribution | localised |
| Formal charges | N: +1 |
| Resonance structures | none |
| Molar mass | 18.039 g/mol |
N Nitrogen 5 valence e− H Hydrogen 4 atoms, 1 valence e− each
How to draw the NH4+ Lewis structure
The reasoning at each step
-
Count the valence electrons
Add up the outer-shell electrons every atom brings, then account for the charge. A 1+ ion has lost one electron, so it is subtracted from it. Skip this and every count that follows will be wrong.
5 (N) + 4 x 1 (H) - 1 (1+ charge) = 8 valence electrons -
Choose the central atom
N is the least electronegative atom here, so it takes the centre. Hydrogen is never central: it can only form one bond.
-
Join everything with single bonds first
Every connection starts as one shared pair. Draw them all before worrying about double bonds - the arithmetic in the next step is what tells you where the double bonds have to go.
4 bonds x 2 = 8 electrons used, 0 left -
Work out how far short you are
Add up what every atom still needs to fill its shell - eight electrons for most atoms, two for hydrogen - minus what its single bonds already give it. Compare that with the electrons you have left. The difference decides everything that follows.
needs 0, has 0, exactly enough -
Check the central atom
N ends up with a full octet. Every electron in the budget is now placed.
N: 8 bonding + 0 nonbonding = 8 -
Check the formal charges
Formal charge is valence electrons, minus lone-pair electrons, minus the number of bonds. They are not real charges, and they are not the ion's charge either - but they must add up to it. Adding these up gives 1+, which is the check that the structure is complete.
N: 5 - 0 - 4 = +1 -
Work out the shape
Count the electron domains on N: 4 bonded groups. A double or triple bond still counts as one domain, because it points in one direction. That gives tetrahedral electron geometry; ignore the lone pairs and the atoms themselves sit in a tetrahedral arrangement.
steric number 4 -> sp3 -> tetrahedral, bond angle 109.5 -
Decide whether it is polar
The bond dipoles are all the same size and the shape places them symmetrically around the central N, so they cancel exactly.
dipoles cancel -> nonpolar
Where the 1+ charge sits
The 1+ charge is written on the N, because that is the atom whose formal charge comes out positive - it is sharing more electrons than a free N atom owns. The charge belongs to the ion as a whole, which is what the brackets around the drawing mean.
People also ask whether NH4+ is polar. Strictly it is neither: polar and nonpolar sort neutral molecules by whether their bond dipoles cancel. A 1+ ion is pulled towards any nearby charge whatever its shape, which is why its salts dissolve in water regardless of geometry. The table below is still worth reading - it shows how unevenly each bond holds its electrons, which is what decides whether the charge ends up spread or concentrated.
| Bond | Electronegativity difference | Character |
|---|---|---|
| N–H | 0.84 | polar covalent |
Common questions
How many valence electrons does NH4+ have?
NH4+ has 8 valence electrons. The atoms bring 9 between them, and the 1+ charge takes away one. 8 of them are in bonds and 0 sit in lone pairs.
Why does NH4+ have a 1+ charge?
The 1+ charge is written on the N, because that is the atom whose formal charge comes out positive - it is sharing more electrons than a free N atom owns. The charge belongs to the ion as a whole, which is what the brackets around the drawing mean. The brackets around the drawing are part of the answer: they say the charge belongs to the whole ion rather than to whichever atom happens to be nearest.
What is the molecular geometry of NH4+?
NH4+ is a tetrahedral ion. The central N has 4 bonded groups, a steric number of 4, which gives tetrahedral electron geometry and a tetrahedral ion.
What is the bond angle in NH4+?
The bond angle in NH4+ is 109.5 degrees. That is the ideal tetrahedral angle, and nothing distorts it here.
What is the hybridization of NH4+?
The central N in NH4+ is sp3 hybridized. Steric number 4 means 4 orbitals have to be mixed, which is exactly what sp3 gives you.
Is NH4+ polar or nonpolar?
Neither, strictly. Polar and nonpolar describe neutral molecules, by asking whether their bond dipoles cancel out. NH4+ carries a net 1+ charge, so it is pulled towards any nearby charge whatever its shape - which is why ionic compounds dissolve in water regardless of geometry. The question the shape does answer is whether the charge is spread evenly: it is, because the tetrahedral arrangement puts every identical bond at the same angle to the others.